gpt-oss-20b vs Muse Spark 1.3 Contributor
Pricing, context window and real answers (September 2026)
gpt-oss-20b (OpenAI) and Muse Spark 1.3 Contributor (Meta), compared as you can actually call them on FastMetal. Both are served from the same OpenAI-compatible endpoint and API key; switching is a change to the model string.
Specs and pricing
 gpt-oss-20b |  Muse Spark 1.3 Contributor | |
|---|---|---|
| Provider | OpenAI | Meta |
| Input (per 1M tokens) | ¥5.36 | ¥17.59 |
| Output (per 1M tokens) | ¥25.02 | ¥35.18 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥18 | ¥35 |
| Context window | 131,072 tokens | 1,048,576 tokens |
| Release date | 8/5/2025 | 9/2/2026 |
| Input modalities | text | text, image, video, file, audio |
| Throughput (p50) | — | — |
| Arena · overall | #252 · ELO 1,317 | Unranked |
| Arena · Japanese | #179 · ELO 1,256 | Unranked |
| Arena · coding | #232 · ELO 1,369 | Unranked |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, gpt-oss-20b: ¥25.02 per 1M output tokens, 29% less than Muse Spark 1.3 Contributor.
- For long documents, Muse Spark 1.3 Contributor: a 1,048,576-token context window against 131,072 for gpt-oss-20b.
- If in doubt, try both on the same key. Switching is a change to the model string, and each is billed at its own rate.
Frequently asked questions
- Which is cheaper, gpt-oss-20b or Muse Spark 1.3 Contributor?
- Per 1M output tokens, gpt-oss-20b is ¥25.02 and Muse Spark 1.3 Contributor is ¥35.18 on FastMetal (yen, before tax), so gpt-oss-20b is cheaper.
- How do the context windows of gpt-oss-20b and Muse Spark 1.3 Contributor compare?
- gpt-oss-20b takes 131,072 tokens; Muse Spark 1.3 Contributor takes 1,048,576.
- Can I use gpt-oss-20b and Muse Spark 1.3 Contributor with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-oss-20b" or "muse-spark-1.3-contributor" as the model. Each is billed at its own rate from the same prepaid balance.
Try both on one API key
Create an account and add credit to call gpt-oss-20b and Muse Spark 1.3 Contributor from the browser chat and the API. No monthly fee.
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